• Season the beef with salt and pepper, then toss it in flour to coat evenly.
• In a large skillet over medium-high heat, melt the butter. Add the beef in batches and sear on all sides until brown and crusty. Transfer the seared beef to a plate and repeat until all the beef is seared.
• Add the diced onions to the skillet and cook for approximately 2 minutes, scraping up any browned bits from the bottom of the pan using a wooden spoon.
• To make in the slow cooker: Transfer the seared beef and onions to the slow cooker. Add the sliced mushrooms, garlic powder, onion powder, dried thyme, dried rosemary, beef bouillon cube, Worcestershire sauce, bay leaf, pepperoncinis, and 355-475 ml (1 1/2 cups-2 cups) of beef stock. Cover and cook on high for 3-4 hours or low for 6-7 hours.

To make in the Instant Pot:

• Add the seared beef and onions back to the Instant Pot. Add the sliced mushrooms, garlic powder, onion powder, dried thyme, dried rosemary, beef bouillon cube, Worcestershire sauce, bay leaf, pepperoncinis, and 355 ml (1 1/2 cups) of beef stock. Cover and select the "Meat/Stew" setting. Cook on high pressure for 35 minutes. Once the cooking time is up, allow the pressure to release naturally for 10 minutes before switching the pressure release valve to "venting" to release any remaining pressure.
• If using a slow cooker, whisk the cornstarch into 3 tablespoons of water and add it to the slow cooker. If using an Instant Pot, stir the cornstarch mixture into the cooking liquid. For both methods, cover and continue cooking for an additional 30 minutes. Season to taste with salt and pepper.
• Serve the delectable beef tips with mushroom gravy over mashed potatoes, noodles, or rice. Enjoy the melt-in-your-mouth goodness!